It was an example of someone inciting irrational fear of a public service which would harm other people, just the way anti-vaccine propaganda does. Going around telling people that there is poison in the public water system is a crime.

A terrorist is a person that is trying to incite fear in a large group of people.

The use of violence and intimidation in the pursuit of political aims.

If someone believes there is a harmful substance in the water supply, and tries to inform people of it, that falls under their freedom of speech. They have a belief, based on some sort of information they gathered, and are simply trying to make that info available.